Heat treatment of a casting elements poured from silumins belongs to technological processes aimed mainly at change of their mechanical

properties in solid state, inducing predetermined structural changes, which are based on precipitation processes (structural strengthening of

the material), being a derivative of temperature and duration of solutioning and ageing operations. The subject-matter of this paper is the

issue concerning implementation of a heat treatment process, basing on selection of dispersion hardening parameters to assure

improvement of technological quality in terms of mechanical properties of a clamping element of energy network suspension, poured from

hypoeutectic silumin of the LM25 brand; performed on the basis of experimental research program with use of the ATD method, serving

to determination of temperature range of solutioning and ageing treatments. The heat treatment performed in laboratory conditions on a

component of energy network suspension has enabled increase of the tensile strength Rm and the hardness HB with about 60-70%

comparing to the casting without the heat treatment, when the casting was solutioned at temperature 520 o

C for 1 hour and aged at

temperature 165 o

C during 3 hours.

Tests concerning EN AC 48000 (AlSi12CuNiMg) alloy phase transition covered (ATD) thermal analysis and (DSC) differential scanning

calorimetry specifying characteristic temperatures and enthalpy of transformations. ATD thermal analysis shows that during cooling there

exist: pre-eutectic crystallization effect of Al9Fe2Si phase, double eutectic and crystallization α(Al)+β(Si) and multi-component eutectic

crystallization. During heating, DSC curve showed endothermic effect connected with melting of the eutectic α(Al)+β(Si) and phases:

Al2Cu, Al3Ni, Mg2Si and Al9Fe2Si being its components. The enthalpy of this transformation constitutes approx. +392 J g-1

. During

freezing of the alloy, DSC curve showed two exothermal reactions. One is most likely connected with crystallization of Al9Fe2Si phase

and the second one comes from freezing of the eutectic α(Al)+β(Si). The enthalpy of this transformation constitutes approx. –340 J g-1

.

Calorimetric test was accompanied by structural test (SEM) conducted with the use of optical microscope Reichert and scanning

microscope Hitachi S-4200. There occurred solution's dendrites α(Al), eutectic silicon crystal (β) and two types of eutectic solution: double

eutectic α(Al)+β(Si) and multi-component eutectic α+AlSiCuNiMg+β.

This paper presents the results of hypoeutectic 226 grade alloy as well as prepared on its basis Al-Si alloy containing Cr, V and Mo. The

additives tested were added as AlCr15, AlV10 and AlMo8 master alloys. Alloys tested were poured into DTA sampler as well as using

pressure die casting. An amount of Cr, V and Mo additives in alloy poured into DTA sampler comprised within the range approximately

0.05-0.35%. Alloys to pressure die casting contained 0.05-0.20% Cr, V and Mo. The crystallization process was examined using the derivative

thermal analysis (DTA). The microstructure of castings made in the DTA sampler as well as castings made with use of pressure die

casting were examined. The basic mechanical properties of castings made using pressure die casting were defined too. It has been shown

in the DTA curves of Al-Si alloy containing approximately 0.30 and 0.35% Cr, Mo, and V there is an additional thermal effect probably

caused by a peritectic crystallization of intermetallic phases containing the aforementioned additives. These phases have a morphology

similar to the walled and a relatively large size. The analogous phases also occur in pressure die casting alloys containing 0.10% or more

additions of Cr, V and Mo. The appearance of these phases in pressure die casting Al-Si alloys coincides with a decrease in the value of

the tensile strength Rm and the elongation A. It has been shown die castings made of Al-Si alloys containing the aforementioned additives

have a higher Rm and A than 226 alloy.

The paper presents an analysis of the effect of shape of primary silicon crystals on the sizes of stresses and deformations in a surface layer

of A390.0 alloy by Finite Elements Method (FEM). Analysis of stereological characteristics of the studied alloy, performed based on a

quantitative metallographic analysis in combination with a statistical analysis, was used for this purpose. The presented simulation tests

showed not only the deposition depth of maximum stresses and strains, but also allowed for determining the aforementioned values

depending on the shape of the silicon crystals. The studied material is intended for pistons of internal combustion engines, therefore the

analysis of the surface layer corresponded to conditions during friction in a piston-cylinder system of an internal combustion engine having

power of up to 100 kW. The obtained results showed important differences in the values of stresses and strains up to 15% between various

shape of the silicon crystals. Crystals with sharp edges caused higher stresses and deformation locally than those with rounded shapes.